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Re: Question about lazy authoring

From: Mark Birbeck <mark.birbeck@webbackplane.com>
Date: Tue, 17 Feb 2009 19:42:08 +0000
Message-ID: <ed77aa9f0902171142p758e385p1f060f84b07417de@mail.gmail.com>
To: John Boyer <boyerj@ca.ibm.com>
Cc: Erik Bruchez <ebruchez@orbeon.com>, Nick_Van_den_Bleeken@inventivegroup.com, Forms WG <public-forms@w3.org>
Hi John,

Although Nick's subject line mentions lazy authoring, I read the
substance of his post to be that you cannot evaluate an XPath
expression unless there is an evaluation context. So either this test
must fail, or we have to work out how to create a default instance. (I
guess that's where Nick drew the connection with lazy authoring.)

So if Erik's suggestion is held over to XForms 2.0 as you suggest,
isn't the answer to Nick's question that the test must be rewritten to
ensure that there is a context of some description? Otherwise,
although it is only a simple call to index(), it cannot be guaranteed
to 'fail consistently' in all implementations.

Regards,

Mark

On Tue, Feb 17, 2009 at 6:56 AM, John Boyer <boyerj@ca.ibm.com> wrote:
>
> Hi Nick,
>
> Why is this a question about lazy authoring?
> The test you identified is testing the IDREF mechanism.  It is not intended
> to test of lazy authoring, so it is a bad test because it will run afoul of
> a lazy authoring problem before getting to the issue it claims to test,
> which is whether the index function returns NaN when it can't find the
> identified repeat.
>
> Erik's point about amending the eval context of an xpath when their is no
> context node would make a good feature/suggestion+test for Section 7.2,
> except it is probably better for XForms 2.0 because in XForms 1.x we have
> Xpath 1.0, which requires a context node as part of the context.  I suppose
> we could make do if all current xpath 1.0 implementations allowed evaluation
> without a starting context node, but this is probably not an issue we have
> to spend a lot of cycles on right now.
>
> For lazy authoring, I think you need at least one real UI binding to be
> expressed because otherwise the lazy authored instance will be empty, which
> is not allowed.  If you squint at the spec in just the right way, you can
> see it producing the same kind of exception as if you had put this into the
> model:
>
> <instance/>
>
> Cheers,
> John M. Boyer, Ph.D.
> STSM, Interactive Documents and Web 2.0 Applications
> Chair, W3C Forms Working Group
> Workplace, Portal and Collaboration Software
> IBM Victoria Software Lab
> E-Mail: boyerj@ca.ibm.com
>
> Blog: http://www.ibm.com/developerworks/blogs/page/JohnBoyer
> Blog RSS feed:
> http://www.ibm.com/developerworks/blogs/rss/JohnBoyer?flavor=rssdw
>
>
>
>
> From: Erik Bruchez <ebruchez@orbeon.com>
> To: Forms WG <public-forms@w3.org>
> Date: 02/16/2009 01:08 PM
> Subject: Re: Question about lazy authoring
> ________________________________
>
>
> XProc solves this issue by saying the following [1]:
>
>   "If there is no binding and there is no default readable port then
> the context node is an empty document node."
>
> Something like this would make sense to me for XForms, but it would
> have to be added to the spec.
>
> -Erik
>
> [1] http://www.w3.org/TR/xproc/#xpath10-processors
>
> On Feb 16, 2009, at 1:32 AM, Nick Van den Bleeken wrote:
>
>> All,
>>
>> Test case 4.7.c has no instance and no controls that have a node set
>> binding, but it has a value attribute on an output control is this
>> supposed to work?
>>
>> In my opinion you can't construct an XPath context because you don't
>> have an instance, because no form controls refer to an instance... I
>> can work around this and create an instance when there is a form
>> control that has a value attribute, but this isn't correct to how I
>> read the spec.
>>
>> What are your opinions about this?
>>
>> Regards,
>>
>> Nick Van den Bleeken
>>
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>



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Received on Tuesday, 17 February 2009 19:42:49 UTC

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